An Indian anti-doping disciplinary panel had ruled earlier this month that the freestyle wrestler was a victim of "sabotage", and cleared him to compete in Rio. Freestyle wrestling starts on Friday.
Yadav had said his supplements and water had been sabotaged and lodged a police complaint against a junior wrestler accusing him of contaminating his food at the Sports Authority of India training centre in Sonepat.
WADA filed an urgent application before CAS to challenge the decision of NADA India to exonerate Yadav following two positive doping tests in June and July.
"The CAS Panel did not accept the argument of the athlete that he was the victim of sabotage and noted that there was no evidence that he bore no fault, nor that the anti-doping rule violation was not intentional," CAS said, announcing a four-year period of ineligibility.
The Wrestling Federation of India has demanded a probe into the doping scandal by the country's top crime-fighting agency, while Yadav has vowed to do everything to clear his name.
"To say I am devastated at the decision of CAS would be putting it mildly," the wrestler said in a statement.
"My dream of competing and winning the country a medal at the Rio Games has been cruelly snatched away from me twelve hours before my first bout, but I will do everything it takes to prove my innocence.
"It is all I have left to fight for."
(Additional reporting by Amlan Chakraborty in New Delhi; Editing by Ossian Shine/Greg Stutchbury)
